Wasn't Miller still doing the covers at that time? The insides are a totally different story.
Edit:
That's a good question. Reading BackIssue #21, Janson states some of the techniques he was using on that issue #190. Here's a quote about pg. 15: "Beautiful design and interesting drawing, but one can't finish this if one can't draw. Klaus kept the design, then added a little drawing, shadows, blacks, and textures. You still can find some kind of Miller's drawing in the final page, but it is clear that the page is a Miller/Janson piece of art. Miller's trust of Janson's work was so real that Klaus was allowed to change whole faces as long as he stayed faithful to Miller's idea."
"Janson embellished Miller's great finished layouts with every tool he could find: brushes, pens, markers, zip-a-tone, duo shade paper, and clothes (for inked effects)."
"By the end of his run, Frank Miller was doing simple layouts on small sheets of papers, a process he began with issue #185. Klaus Janson was drawing, inking, and coloring the book."
Janson goes on to talk about texture and color. Seems like the kind of things one would do when working on two different pages to create one image. Again, nothing concrete but puts the cover(s) in a different perspective.